In recent years, crude oil containing sulfur imported by China has been growing year by year, and that imported in 2002 reached 6.9×107 tons. Due to the high content of sulfur in the crude oil produced by Arabian countries in Middle East, the proportion of imported crude oil containing sulfur to be processed has been increased year after year. The increase of sulfur in the circulating hydrogen of a hydrogenation process, depending on the increase of sulfur in crude oil, leads to the growth of the density of the circulating hydrogen and the energy consumed by the circulating hydrogen compressor, and the decrease of the purity of the hydrogen gas as well as the useful life and the activity of the catalyst.
The existing hydrogenation devices typically has the problem that circulating hydrogen, liquid hydrocarbons, diesel oil, waste water containing sulfur and low-pressure separator gas tend to entrap such dispersion-phase particles as heavy hydrocarbons, amine, water, catalyst and the like, which not only results in the increase of the consumption of additives and the loss of starting materials, but also results in serious damage to the down-stream key equipments in terms of long cycle run. The entrapment of heavy hydrocarbons in circulating hydrogen, liquid hydrocarbons and low-pressure separator gas may cause the circulating hydrogen, the liquid hydrocarbons and the solvent in the desulfurizer for the low-pressure separator gas to froth and cause the abnormal loss of amine solution. The amount of amine solution lost varies significantly from a minimum of 0.05 kg/ton dry gas or 0.1 kg/ton liquefied petroleum gas to a maximum of 1.0 kg/ton dry gas or 10 kg/ton liquefied petroleum gas, depending on the specific manufacturing device. The abnormal loss of amine solution may aggravate the burden of the waste water disposing plant directly by inflicting secondary contamination on the waste oil system. Furthermore, the solution and the dust entrapped in the circulating hydrogen constitute a great threat to the long cycle run of the compressor. The problem currently existing in nearly all refiners to various extents is that circulating hydrogen, liquid hydrocarbons, diesel oil, waste water containing sulfur and low-pressure separator gas entrap solution and dust, which may boil down to non-homogeneous separation, and is in an urgent need to be attacked in design and operation.
In prior processes, a coalescer has been chosen to remove the solution and the dust entrapped in circulating hydrogen, liquid hydrocarbons, diesel oil, waste water containing sulfur and low-pressure separator gas. However, the long cycle run time of only one year presently guaranteed by coalescer providers around the world in the form of technical agreements cannot meet the demand of SINOPEC who expects the maintenance to be done every three years. If the guaranteed long cycle run time is three years, the diameter of the coalescer must be increased to that of the reactor. This means higher cost and more occupation of ground. Additionally, the coalescer must be equipped with a bypass system, thus disagreeing with the general design criteria for high-pressure systems. As revealed by an investigation, the heavy hydrocarbons coalescer for circulating hydrogen in Maoming Branch of SINOPEC can only run for one year before maintenance rather than three years as demanded by long cycle run.
With respect to the entrapment of amine solution in circulating hydrogen, liquid hydrocarbons and low-pressure separator gas at the outlet of the desulfurizer, a sedimentation tank is generally designed to remove the solution and the dust. However, desulfurization with amine suffers from a troublesome problem yet to be solved thoroughly, i.e. so called “solvent frothing-up” or the quick loss of amine solution. Amine solution is prone to froth per se, and in the cases where the contents of heavy hydrocarbons such as C5, impurities such as HSS and iron rust (e.g. due to incomplete pre-treatment of the system by scrubbing with alkaline solution before the newly-built equipment is put into operation) in the system are high, frothing will be initiated. Though a defrother may be used to temporarily refrain the amine solution froth induced by such frothers from growing further, froth plugging that is a blank wall will come into being if the froth develops to certain extent, and thus the compressor will not run properly.
Therefore, future effort is undoubtedly directed toward the development of a non-homogeneous particle separating system which can be used to treat circulating hydrogen, liquid hydrocarbons, diesel oil, waste water containing sulfur and low-pressure separator gas from a hydrocracking device with high efficiency, safety, environmental compatibility and long operating cycle.
Microcyclone separators of 5 mm, 10 mm, 15 mm and 25 mm were designed by School of Mechanical and Materials Engineering of Washington State University in USA. A cyclone separator of 19 mm might achieve a separation efficiency of 95% for 3 μm bio-aerosol particles, and over 80% for 2 μm bio-aerosol particles. However, this technology, still in its experimental study phase, faces a lot of difficulties to be overcome before it is applied to industry.
Among the considerable efforts made by Chinese researchers in vortex separation industry, Chinese patent CN 200995173Y disclosed a gas-liquid vortex separator, and CN 2912804Y published a multi-column-cone vortex separator for liquid-liquid separation, the main body of which was composed of several column sections and cone sections, which were connected alternatively, with a tail pipe attached thereto. Although the application scope of vortex separation technologies has been under continuous expansion due to the innovation in the configurations of vortex separation devices, vortex separation processes are still subjected to technological limitation when the density difference is small and the separation precision is required to be high.
Anyway, due to the foregoing problems in the prior art, no way has been found so far to purify a circulating hydrogen mixture containing sulfur to a satisfactory extent, and thus the expectation of clean production in the petrochemical engineering sector is far from being satisfied. Therefore, there is an urgent need in the art for a process for treating a circulating hydrogen mixture containing sulfur at low cost and with good effect, and a device for the same.